1. Field of the Invention
The present invention relates to a charger for rapidly charging a lithium ion battery.
2. Related Background Art
The following two methods have been used in the past as charging methods for a lithium ion battery.
Referring to FIGS. 10 to 13, configurations and operations of prior art chargers are explained.
FIG. 10 shows a circuit block diagram for illustrating a configuration of a prior art charger.
In FIG. 10, numeral 101 denotes a rectifier/filter circuit for rectifying and filtering AC 100 volts, numeral 102 denotes a constant voltage/constant current regulation circuit, numeral 103 denotes a switching circuit, numeral 104 denotes a timer circuit and numeral 105 denotes a lithium ion battery.
FIG. 11 shows a voltage-current characteristic of the constant voltage/constant current regulation circuit 102 shown in FIG. 10 wherein an ordinate represents a voltage V and an abscissa represents a current I.
As shown, in the constant voltage/constant current regulation circuit 102, a charging current is limited to be no greater than a predetermined current and a charging voltage is limited to be no greater than a predetermined voltage and the charging current is supplied to the battery 105 from the constant voltage/constant current regulation circuit 102, and when a predetermined time period which is preset by the timer circuit 104 has elapsed, the charging is stopped by opening the switching circuit 103 to shut off the charging current.
FIG. 12 shows a circuit block diagram for illustrating a configuration of another prior art charger. The like elements to those in FIG. 10 are designated by the like numerals.
In FIG. 12, numeral 106 denotes a voltage detection circuit for detecting a battery voltage. When it detects a predetermined battery voltage (point A in FIG. 13), it opens (turns off) the switching circuit 103 to shut off the charging current to stop the charging.
FIG. 13 shows a characteristic chart of a time shift of a charging voltage and a charging current in charging by the prior art charger, in which an ordinate represents a charge and an abscissa represents a time.
In FIG. 13, when the battery voltage approaches a full charge, it becomes constant and the charging current starts to decrease.
However, in the charger shown in FIG. 10, the predetermined time preset by the timer is needed without regard to the remaining amount of charge, which is loss of time for a user and may lead to overcharging.
Further, in the charger shown in FIG. 12, when the charging is stopped upon the detection of the voltage at the point A as shown in FIG. 13, the charged amount reaches only approximately 90% of the battery capacity. The user cannot detect the current charge amount during the charging.